From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [PATCH v2] KVM/PPC Patch for KVM issue in real mode Date: Wed, 30 Nov 2016 14:05:06 +0530 Message-ID: <8760n5icw5.fsf@linux.vnet.ibm.com> References: <20a3e138-8a6e-6ad8-b9ba-ec8332f011a5@gmail.com> Mime-Version: 1.0 Content-Type: text/plain Cc: linuxppc-dev , Paolo Bonzini , Paul Mackerras , Radim To: Balbir Singh , kvm-ppc@vger.kernel.org, kvm@vger.kernel.org Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:42027 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755074AbcK3IfP (ORCPT ); Wed, 30 Nov 2016 03:35:15 -0500 Received: from pps.filterd (m0098409.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uAU8XfwL043055 for ; Wed, 30 Nov 2016 03:35:15 -0500 Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) by mx0a-001b2d01.pphosted.com with ESMTP id 271qjerarg-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 30 Nov 2016 03:35:15 -0500 Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 30 Nov 2016 01:35:14 -0700 In-Reply-To: <20a3e138-8a6e-6ad8-b9ba-ec8332f011a5@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: Balbir Singh writes: > Some KVM functions for book3s_hv are called in real mode. > In real mode the top 4 bits of the address space are ignored, > hence an address beginning with 0xc0000000+offset is the > same as 0xd0000000+offset. The issue was observed when > a kvm memslot resolution lead to random values when > access from kvmppc_h_enter(). The issue is hit if the > KVM host is running with a page size of 4K, since > kvzalloc() looks at size < PAGE_SIZE. On systems with > 64K the issue is not observed easily, it largely depends > on the size of the structure being allocated. > > The proposed fix moves all KVM allocations for book3s_hv > to kzalloc() until all structures used in real mode are > audited. For safety allocations are moved to kmalloc > space. The impact is a large allocation on systems with > 4K page size. We did such access using *real_vmalloc_addr(void *x). So you are suggesting here is we don't do that for all code path ? Do you have a stack dump for which you identified the issue ? > > Signed-off-by: Balbir Singh > --- > Changelog v2: > Fix build failures reported by the kbuild test robot > http://www.spinics.net/lists/kvm/msg141727.html > > arch/powerpc/include/asm/kvm_host.h | 19 +++++++++++++++++++ > include/linux/kvm_host.h | 11 +++++++++++ > virt/kvm/kvm_main.c | 2 +- > 3 files changed, 31 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h > index f15713a..53f5172 100644 > --- a/arch/powerpc/include/asm/kvm_host.h > +++ b/arch/powerpc/include/asm/kvm_host.h > @@ -734,6 +734,25 @@ struct kvm_vcpu_arch { > #define __KVM_HAVE_ARCH_WQP > #define __KVM_HAVE_CREATE_DEVICE > > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE > +#define __KVM_HAVE_ARCH_VZALLOC_OVERRIDE do we need that OVERRIDE ? We usually have HAVE_ARCH_KVM_VZALLOC or just say #ifndef kvm_arch_vzalloc ? > + > +/* > + * KVM uses some of these data structures -- the ones > + * from kvzalloc() in real mode. If the data structure > + * happens to come from a vmalloc'd range then its access > + * in real mode will lead to problems due to the aliasing > + * issue - (top 4 bits are ignore). > + * A 0xd000+offset will point to a 0xc000+offset in realmode > + * Hence we want our data structures from come from kmalloc'd > + * regions, so that we don't have these aliasing issues > + */ > +static inline void *kvm_arch_vzalloc(unsigned long size) > +{ > + return kzalloc(size, GFP_KERNEL); > +} > +#endif .... -aneesh